1. Field of the Invention
The subject matter of this invention is contact lenses and intra-ocular lenses, and relates more particularly to a diffractive bifocal contact or intraocular lens and to a method of its manufacture by excimer laser ablation. In this specification, it will be convenient to use a single term to mean both "contact lens" and "intra-ocular lens". The term "eye lens" is hereby coined for this purpose.
2. Background Information
The adaptation of a phase zone plate for use as a diffractive bifocal contact lens was apparently first reported in 1966 by G. Forst in Der Augenoptiker. The lens was made by drawing the desired zone pattern on paper, producing a photographic negative of this pattern, projecting an image of the negative on an emulsion surface on the corneal bowl, and developing the photo-emulsion. The Forst paper concludes that the feasibility of a diffractive bifocal contact lens, for special cases, is demonstrated. The fabrication of such a lens accurately, reproducibly, and in acceptable wearable form, has however remained a problem until the present.
U.S. Pat. No. 4,642,112 was issued on Feb. 10, 1987 to Michael H. Freeman. It discloses a contact lens having the appropriate curvatures providing basic refractive power for ordinary or distance vision; with a transmission hologram formed on the lens to provide diffractive power which is additive to the refractive power for near vision.
Generally, the etching of polymers by excimer lasers has been widely reported in the literature. Specifically, the production of diffraction gratings by laser etching of photo resists is also well known to the art.
Finally, European Patent Application No. 0,264,255 was published on Apr. 20, 1988 and discloses an excimer laser optical system for cutting and shaping contact lenses and like objects.